Hitherto, a semiconductor wafer (sometimes simply referred to as “wafer”) composed of silicon or gallium arsenide is mounted on a carrier such as a lead frame or a module substrate after a large wafer is cut into a small wafer (die). At the mounting, the wafer is adhered through an adhesive such as an epoxy resin. However, with the progress of miniaturization and thinning of the wafer, it becomes difficult to apply an appropriate amount of the adhesive to the small wafer without damaging the wafer.
With respect to the above-described problem, there is a method of mounting a semiconductor chip after attaching a sheet-shaped die-adhering adhesive layer to a carrier in advance. However, an increase in step number and facility is indispensable since it is necessary to cut the die-adhering adhesive layer into the same size as the size of the semiconductor chip in advance.
Furthermore, various wafer-adhering adhesive tapes simultaneously having a fixing function at wafer cutting and a die-adhering function have been proposed. That is, a semiconductor chip with a die-adhering layer can be obtained by providing a die-adhering layer on a pressure-sensitive adhesive layer of a dicing tape that is a wafer-fixing pressure-sensitive sheet, placing a semiconductor wafer thereon, cutting the wafer into small pieces, and subsequently picking up semiconductor chips through peeling them between the pressure-sensitive adhesive layer and the die-adhering layer.
The above-mentioned method is a production process which enables so-called direct bonding and improves production efficiency of the semiconductor chip to a large extent but there are required such conflicting functions that a wafer should be fixed so as not to cause chip fly in a cutting step and the chip should be easily peeled between the pressure-sensitive adhesive layer and the die-adhering layer so as not to induce picking-up failure in a picking-up step. To deal with the problem, there have been proposed various pressure-sensitive adhesive tapes having a mechanism of changing a pressure-sensitive adhesive force between the wafer-fixing pressure-sensitive adhesive layer and the die-adhering layer by imparting an external stimulus such as heat or a radiation ray (see e.g., Patent Documents 1 to 4).
For example, Patent Document 1 (JP-A-2-248064) discloses a film wherein a dicing tape having a pressure-sensitive adhesive layer where a radiation ray-curable additive is added to a usual pressure-sensitive adhesive is laminated with a die-adhering layer in an integrated fashion. After diced, the wafer is irradiated with a radiation ray to cure the pressure-sensitive adhesive of the dicing tape and lower the pressure-sensitive adhesiveness and then a semiconductor chip is peeled off at the interface between the die-adhering layer and the dicing tape in a perpendicular direction to pick up the wafer with the die-adhering layer. However, in the method of using radiation ray irradiation, it is difficult to balance the holding force at dicing and the peeling ability at picking-up. For example, in the case of a large semiconductor chip having a size of 10 mm square or more or an extremely thin chip having a thickness of 25 to 50 μm, it is impossible to pick up the semiconductor chip by a common die bonder.
Moreover, Patent Document 2 (JP-A-3-268345) discloses a method of laminating a die-adhering layer on a pressure-sensitive adhesive layer containing thermally-expandable fine particles but there is a case where fouling occurs on the peeled surface of the die-adhering layer through cohesive failure of the pressure-sensitive adhesive component. The fouling of the die-adhering layer may cause insufficient adhesion to the lead frame, module substrate, and the like or generation of voids at the interface between the die-adhering layer and the lead frame, module substrate, and the like during a reflow step after the semiconductor chip is mounted.
Furthermore, Patent Document 3 (JP-A-2004-186280) proposes a method wherein a gas-generating agent, which generates a gas by an external stimulus such as heat or an ultraviolet light, is dispersed into the pressure-sensitive adhesive layer of a pressure-sensitive adhesive sheet. According to this method, the gas generated by the external stimulus invades into the interface between the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet and the die-adhering layer and presses the layers to peel off a part of the interface between the pressure-sensitive adhesive sheet and the die-adhering layer, whereby it becomes possible to peel the pressure-sensitive adhesive layer from the die-adhering layer easily.
Patent Document 4 (JP-A-2006-128621) proposes a method of controlling elastic modulus of the die-adhering layer and peeling strength between the die-adhering layer and the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet for easily peeling the pressure-sensitive adhesive layer from the die-adhering layer. However, depending on the composition of the base polymer in the pressure-sensitive adhesive of the pressure-sensitive adhesive sheet, there is a case where the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is strongly adhered to the die-adhering layer and the picking-up is not satisfactorily performed.